<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>

        .div1{
            width: 100px;
            height: 100px;
            background: red;
        }
        .div2{
            width: 50px;
            height: 50px;
            background: green;
        }
    </style>
</head>
<body>

        <!--2, 类选择: 通过标签的类名(class), 把css样式和对应的html代码关联起来-->
        <div class="div1">
            div1
        </div>
        <div class="div1">
            div1
        </div>

        <div class="div2">
            div2
        </div>

</body>
</html>
